Mesa MarkV / Saturation 'mod'

[bandit2013]

I have the 12AT7 in V4. The lower gain will roll off some of the higher order harmonics caused by the first preamp tube in the high gain circuit which is actually V5. I also have an SPAX7 in V1. Everything else is stock. Why I like this so much, it gives the amp some lower mids on CH3 that I felt were missing. As well as the nice tone I am hearing (no more ice pick) It sounds just like the JP-2C. The Mark V CH3 mark iv voice now sounds identical to the JP-2C CH2, the CH3 extreme sounds very much like the JP-2C CH3. I ran both amps side by side and found it difficult to distinguish between the two with the mod on the V. Also the 5BEQ seems to be more reactive than it was probably due to the tonal change of the CH3 gain stage.

Ever since I got the JP-2C, nothing else seemed to satisfy me (with the exception of the TC-50). Now the Mark V is on par with the JP-2C so I will keep it. Was planning on selling it. At least I was able to get the tone out of the Mark V but this was unexpected.

 

[APEMAN]

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[bandit2013]

Sorry for soap box......
Out of my collection of amps ranging from the Mark V, Roadster, RA100, JP-2C and finally the TC-50 I can relate one feature about the Mark V over the others, it is more versatile in terms of preamp tube selection. For the Roadster, there are limits in what tubes to employ as it has two cathode follower circuits that will kill some tubes (generally the Russian). With that amp you are limited to V1 and V2 for tone shaping. As it seems V1 with a tung sol usually frees the amp from being bass dependent. RA100 has two independent preamp sections and the same applies to the TC-50. The clean channel has two tubes dedicated for that purpose only, the Hi/Lo channel uses two other independent tubes for the gain channels. In essence both amps use different tubes for the first gain stage. This may give you freedom to choose tubes to characterize the clean vs gain channels. For the RA, there is some effect but limited. TC-50 and the JP-2C are tightly tuned to perform their best using the Mesa 12AX7. I had tried a few preamp tubes other than the Mesa and the end result was not very rewarding. This leaves us with the Mark V which responds quite well to various tubes installed. It is amazing what a singe tube can do for each channel but there are some positions shared by all. Since V2 only affects the CH2 circuit, I personally prefer the old Mesa (Chinese 12AX7A that has the square foil getter) when I am using other than stock power tubes. As of recent times, I returned the Mark V to stock tubes as I planned on selling the amp. I do not mind the tone of CH2 with the stock tube but the added gain from the old Mesa tube improves the crunch tone closer to the Mark IV mode as that is what I was using it for. I have done so much tube rolling in this amp in hopes to reduce the higher order harmonics produced during the hard clip and cut that made it impossible to enjoy along with the lack of tighter bottom end and lower mid range tone that was missing from the Mark IV mode when using 90W power. Sure I had the Mark IV amp too and at the same time I had the V. I just did not like Rhythm 2 on the Mark IV as it was awful though the combo. Sounded good though the 412 cabinet though. Almost use the Head shell for the Mark IV chassis but sold it to someone who was converting their Mark V combo to a head. From my many years with the Mark III (24 to be exact) had that specific tone once you figured out how to dial it in that had me hooked for life and a believer that no other amp will satisfy me other than a Mesa Boogie. The Mark IV combo was a bit of a disappointment and perhaps it may have been the MC90 speaker. Tone was a bit honky and the OS Recto 412 cab just sounded flubby. One I figured out how to run the Mark IV with the combo speaker I was happy. I actually thought the Mark V had a better tone but that was with the amp in the 45W power and the power switch set to variac. I found the 90W power mode to be less forgiving, extremely brittle and more times than most I would get that breaking glass sound ringing in my ears. The Roadster and the RA100 were my relief from this issue. Converting the Mark V head to a combo also helped to curb the ice a bit since I could select any speaker to shovel in the shell but that turned out to be following a balloon of a different color (never ending quest). I finally decided to put the amp up for sale so I bought the MC90 for the combo and well here we are... What really pushed the want to sell the Mark V was the invasion of the JP-2C into my home. Now that has the tone I have been searching for as long as I owned a boogie. I would agree that the CH2 sounded better in crunch or Mark I mode. Edge mode just never thrilled me as it was just as brittle or worse than CH3 with all of its voices. CH1 tweed was also brutal. With this amp I have noticed that the SPAX7 seems to fix the brittle ness with the tweed setting, still do not like edge but I can now use it with out hating it. I just could not use CH3 with a gain setting more than 10AM, presence either as low as it could go and the treble at 10am or lower. Extreme mode with the preset EQ on the 5BEG was the worse in terms of brittleness (did not matter if I used EV or V30). The change in V4 actually make CH3 sound more like the iconic Mesa tone that rivaled most amps since the dawn of the Mark IIC+. If the JP-2C is anywhere close to that I will bow down to the creator as there is a god answering guitar gear prayers. Since the V4 Change, it has made me change my mind about loosing a bad marriage. Mark V is back to keeper status. Now I can boost the gain, adjust the presence to taste and push the treble past noon and tailor my tone the way the amp should have been in the first place. This may only be the beginning as there may be something else to tune your amp with, different tube in V1 or else where. At least the brittle monster is dead and I can focus more on playing the guitar rather than avoid using a great amp because of a character flaw. I am not fond of pedals on the front end of the amp but the grid slammer and even the flux drive seemed to help give to the amp what CH3 was missing. Now I do not need them but will have to see how that will work out. I have used them with the JP-2C only to find more amazing tones.

 

[IronSean]

Hey Bandit,

Would love to get hold of some =C='s but doubt i could justify the cost of them to the wife now. Shame as they seem like they had a good thing going there. Out of all the new production tubes they seem to be the only one's which are widely regarded as great. Wish i could afford them. Next best option seems to be the TAD 6L6 GC's, can get a matched quad for around £80 here in England, =C='s are more then twice that! Why did they get so expensive? Supply and demand? Even so, £80 is going to be hard to find at the moment, young family and all that, so will have to wait I'm afraid. Full bodied and bold sounds like i'd love them with the Mark V the way i have it now. Maybe I'll get to treat myself in a few months time if i keep my overtime up. In the meantime, I'm more than happy with the stock 6L6's and the EL34ii's as you might have guessed haha.

The SED =C='s may have been new production, but they're out of production now so stores have raised prices accordingly as what they have is now essentially NOS and all they'll be able to get.

 

[bandit2013]

I personally would not waste the money on the SED tubes that are out in the market places at the moment. Most of them are seconds' and may have mechanical issues. Last set of the =c= I bought were noisy (rattled). Bummer than I only ever bought two complete quads of the 6L6GC (got a good deal on 1990's which are the best I have ever used, last set is okay, they sound good but for low volume playing the tube rattle gest on my nerves. Same is true about the EL34's I bought at the last chance time a couple of years ago right after they stopped production...

Good alternative: Tung Sol 7581A. The Svetlana's will sound bright in the Mark V (have a quad of those too and are similar to the Tung sol but different construction). I have not gone that far on power tubes as there seems to be more flavors out there now. One reason why I changed the fixed bias in the amp was the drop in production of the SED =C= consumer grade tubes. They were the only tubes that never red plated (except for the Tung Sol 7581A) Mesa tubes would be burning away in a few hours of use as was everything else. Thought that may have been the cause for the brittleness of the amp on all three channels, nope, it was mostly the preamp. Minor change in one resistor (not recommended to mod the amp in this manner) and I could use the Mesa tubes or others that failed within 2 to 3 hours of use. Since I did it, I have had a set of Mesa STR440 6L6GC and no red plating. Same color code as the one's I killed early on before finding the SED tube. Perhaps the bias diode D21 is bad since the specific voltages were not as stated in the schematic at full power but with variac power they were.

Tip, if you find the JAN/Phillips a bit to warm in tone, use the Mesa 12AT7 as it will be brighter in tone however the fundamental change is about the same. I personally prefer the Jan/Phillips. Have an NOS RFT as well but I feel the JAN phillips sounded better (also meets military standards due to the JAN designation)

 

[Wayno]

Thanks guys,

Why would you end production of one of the few new production valves that actually had a good reputation? Seems like very poor business sense to me? Would have made much more sense to cut a deal with one of the major amp manufacturers I would have thought? Unless there was some other reason, politics probably.

Going to return some of the stock mesa 12AX7'S to the amp and just run something like V4 - 12AT7 and one of the Sylvania's in V1 to see what it sounds like. Money's going to be at a premium for some time so don't wanna burn them all out together. That way I'll have a spare of each. Probably still try the Tungsol in V2 just for kicks. Hope the amp stays sounding the way it does currently as it's incredible right now.

Hope everyone is well.

Wayno.

 

[bandit2013]

Wayno,
I have read all about what went down with Svetlanan Electron Devices. In short, audio tubes are not their main business but you have to keep in mind this is not like a US type company. SED (for short) sold the US trade name "Svetlana" to the New Sensor company (they use a different manufacturer who makes majority of the Russian tubes for the US and other Markets. Tubes marked now as Sveltlana with the large S logo (what was used by the original SED company so they changed their logo to =C=). Due to the sale of the trade name, SED could not sell products in the US. They were basically banned from what I understand so do not quote me on facts please. You can do a search on the subject which is a deep rabbit hole to get into now a days. It is what it is, the final art of creating a simple product has been lost. For some reason I think part of it is the dual getters but there is more to it than a meager internal feature. SED claimed that they could no longer resource the quality of glass that was required to make the tubes. As the story goes, it was the end of the line for that part of the production and I would assume the cost to drop the production was probably less than retooling. So what ever the reason it does not need to make any sense. With some of the Mesa amps, the tubes really made a difference as I found it hard to find similar gain characteristics that had that 3D quality. Odd thing though, the Roadster loaded with Stock power tubes sounded much better as it had its own 3d gain character that I could not get from the Mark V unless I had the =c= in it. What does come close is the Tung Sol 7581A. I had tried the non A version and they were great for a while until the tone shifted. Even after I burned many hours on them (4 to 5 months if not longer) I was pleased they lasted longer in my Mark V than the stock tubes. Never red plated them. Quality was there in spades just like the SED. Note that even the Mark IV was able to get a red tint on the plate seams with the SED but you had to really drive the amp hard. The Mark V seemed to eat tubes right from the start. Thus far the long term survivors in the amp was the SED, Tung Sol and the TAD. Everything else had a very short life. (one last note, the KT77 and all other EL34 never had this issue at full power but now stated in the download manual it is better to use variac power with EL type tubes). I still have both quads of SED tubes and they still sound awesome. I have recently adopted the Mesa STR440 tubes as they have their own character to them but had to adjust the bias resistor to use them (kept the amp from red plating but it was not just limited to the Mesa tubes either, perhaps there was an issue with that one part and as it got hot the bias shifted, not really sure, odd thing I was red plating the center pair using 45W mode and variac power). I basically replaced the one 82k resistor with a 91k but may go and try a closer value to the stock part eventually. I do not want it adjustable as it only applies to the 6L6 bias and would not affect the EL34 bias all that much based on the circuit design. I measured the bias voltage before and after and did not see any change but could have been due to limits of the meter. A scope would have been a better choice to use). No matter. I did not see any benefit in having an adjustable bias pot with this amp.

 

[bandit2013]

I finally got around to the Acid test. No I did not take acid. :shock: I wheeled in the OS Recto 412 cab with original speakers. I found the V30 with the Mark V to have been more brutal and accentuated the ice pick to breaking glass tone. WOW, my ears must have been deceiving me as I was in heaven. The mod does make a huge difference. The horizontal or vertical 212 cabs have nice deep tone which make them sound huge. The 412 cab is a bit different and can be extremely bright once you get the amp to the sweet spot. The mod does not kill the top end by any means, it is present and abundant but the lower mid peak as well as more roll off on the upper harmonics is more enjoyable on all voices of the Mark V channel 3. Woot Woot...

Jan/Phillips placed in V4 puts the boogie back into your boogie (Mark V that is). CH1 and CH2 remain the same. The reverb may be slightly different but still sounds the same. Not louder so no worries there.

 

[espexp]

I'm officially a believer! I put a Jan/Phillips 12at7 in the V4 position and ....wow! Channel 3 on Mark IV, 45 watts(variac), in Triode is just pure heaven. This is the heavy Mark tone I've been looking for. With a moderate V (nothing boosted or cut more than half way)on the EQ and the mids at around noon there is a character to the sound that is incredibly pleasing and organic/natural. The difference is huge, more than I ever would have expected from changing 1 preamp tube.

I was having a hard time before the change, switching back and forth from IIC mode and Mark IV mode, never quite finding what I was looking for. It would either get ice-picky or too scooped sounding as I got closer to what I wanted to hear. Now I'm a very happy Mark V owner.

Thank you APEMAN and Bandit!

 

[Wayno]

Thanks for the low down Bandit. Is a shame that had to happen with the =C=. Would have liked to have tried them, heard lots of good things. Nevermind. Look forward to hopefully being able to try the TAD 6L6's.

Roll on the weekend so hopefully I can try get another couple hours in the garage. Rock on you good people.

 

[bandit2013]

Organic, that is the best term that defines what CH3 become with a change in one preamp tube.

Fluidic, sustenance, and commanding also comes to mind. Not thin stale or lifeless. It really is not all that bad without the change, and many 12AX7 tubes will aid in the frequency response that may have a bit more top end roll off but they do not seem to help with the lower mid to center midrange that seems to be getting notched out. I never really thought the Mark IV mode was exact but with the change in V4 to a 12AX7 it gets farther from the Mark IV and way closer to the JP-2C. The IIC voice sound great too. Extreme is also reveling and screams JP-2C CH3 of course with some limitations. If you want the shred mode you may need a grid slammer pedal or other external OD with adjustable tone control. Since I have the Grid slammer, need to see what it will do up front. Before the Mod, the Grid slammer helped greatly as it introduced the mids that were missing and balanced out the tone on CH3.

 

[APEMAN]

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[bandit2013]

With the change in one tube alone, I am overjoyed on the result. At least it is not a permanent mod and can be returned to stock with a twist, pull, push (if you can get the tube in that easily) push and twist. It is only like changing a light bulb when the bulb is hot but you can wait for things to cool down.

Now I have no desire to use other tubes than the Mesa STR440. Hmm, I do have many to go through and wonder what............too much to do.

I have both grid slammer and Flux drive and have tried both (independently) on the JP-2C and the Mark V. The grid slammer effect on CH3 of the Mark V had the same qualities of the JP-2C without any effects. It did help with some of the brittle tone but did not correct for it. Flux drive was similar as that too picked up the lower midrange but also added more distortion. IMHO, I ran each into the JP-2C only to discover there is more to that amp and in either case the additional pre gain or OD was just as pleasing to the ear with out them in use. Do I like it with or without, even if it is not needed. I need to revisit the grid slammer on the V after the mod.

Everything is subjective. If you want more bite (assuming you want the effect brighter) use the Mesa 12AT7, fundamental is there but more crispy. I prefer the warmer tone of the JAN 12AT7. Speaker choice will also determine to what level of cut you may get in the mix or if you will drown. I would suggest this if you find your amp too brittle for enjoyment, or if you want your Mark V to sound like the JP-2C but only effects CH3 as CH2 and CH1 are unaffected.

Need a recording of before an after. That may prove more convincing that the written word unless you listen to it on a cell phone or cheesy internal PC speaker that only does beeps and buzzer sounds effectively.

 

[bandit2013]

I spent a little time comparing the cascaded gain stage of CH3 on the Mark V to the similar gain stage on the Mark IV (schematics for both amps). There is a minor difference between the two amps in this region. Mark IV circuit on the lead tube gain stage has a small capacitor that ties the cathode to the grid which may form a positive feedback loop to increase the gain saturation of the stage. The second tube gain stage does not have this capacitor which may explain why this amp does not get so brittle in character and retains more frequency range in its output. The Case of the Mark V is similar to the Mark IV but on the second gain stage the cathode to grid capacitor is present. My assumptions if correct this additional positive feedback may contribute to higher order harmonics that contribute to the brittle tone. I am no tube expert but since the feedback is connected to the cathode to grid it cannot be negative feedback as that would require it to be connected to the plate vs cathode on a common cathode circuit. Positive feedback is not a common thing to do as this may result in loss of gain control. Typically there is an intrinsic capacitance that between the grid and cathode as well as between grid to plate and plate to cathode as part of the model used for simulation purpose and to understand the tube characteristic. I am only assuming this to be a form of positive feedback but it may be a means to increase the intrinsic capacitance between cathode and grid for a change in tone control. Since the signal at the cathode will be in phase with the signal on the grid, I am to assume it is positive feedback. Signal on the plate will be inverted.

One important note about the schematics and actual circuit board assembly. Just because a component is shown on the schematic does not mean it is actually on the PCB assembly. Sometimes designers leave component footprints in place in a particular circuit but may not be populated in the final assembly as it may have been deemed not necessary. Only way to confirm is to find the part reference designator on the PCB to confirm it is in the circuit. Also since I am uncertain its actual function (positive feedback is assumed) do not go looking for it as it may not even be there. I was just trying to correlate the differences between the Mark V and the Mark IV, and at one time I had both amps but preferred the Mark V over the Mark IV for its features and simplicity to dial in the CH1 and CH2 separate from each other. Mark IV shared common tone controls on the RHY1 and RHY2 that made some settings difficult to obtain for a good 3 channel amplifier. Still the Mark IV was better than the Mark III at channel separation (also needed a decoder ring to decipher the difference between clean and blues and everything else as the tone controls were common on all channels.).

 

[bandit2013]

Well I tried to capture the differences in a recording. Did not turn out so great but some of the differences you can hear. The top end frequencies seemed to have eluded the microphones for the most part but general tone is there. I may have had the bass dialed in a bit too rich. Also had some issues when switching over to the Extreme mode as the inputs were getting clipped so the mixer preamps were adjusted to compensate. I left the EQ as is. I did a little post eq that affected the entire recording. Also did a bit of compression when mastering the mix as the original signals seemed a bit on the low side. I did mark the sections with comments to identify the CH3 voices and where the JP recording starts. What you are missing is the feel, the recording is close enough but not quite the full experience.

https://soundcloud.com/user-353100000/markv0001wav

 

[bandit2013]

Keep in mind this is the first time I used the mixer for recording the guitar. The Sennheiser e609 need far more adjustments on the pre EQ settings than did the Audix D2 regarding the mixer. Actually the D2 by itself sounded the best. D4 was similar but deeper in tone. First time to use the Drum mics on guitar cab. Perhaps they were right that they will sound great as they are already pre eq'd to eliminate the low mid drone you normally get with acoustic drums. I am not too fond of the SM57 but I do have one. Thought the Sennheiser was better now I think I prefer the Audix D2.

 

[bandit2013]

It may be harder to hear the differences in the recordings but if you jump around with your cursor and click on the sound wave you can year the similarities in a different way than having to listen to the entire thing... Also the levels during recording were not managed properly. A DAW would have made things a bit easier. The in the room experience was more revealing than the recording. I believe the master control was at noon on the Mark V as I was using the FX loop. Probably what I should have done was record one voice with two different tubes and not adjust the settings on the mixer or master volume on the amp.

 

[soundbee]

Although it's not "perfect"... your clips do a great job at showing the difference. 12AX7 and 12AT7 in v4 differences (to me) are most noticeable in IIc mode, still prevalent in IV mode and not-as-much in Extreme. As you say, bouncing between related clips is really the way to compare these. But the JP2C clips on the end = yum!!!! There's really something a bit different there. I think there's a JP2C in my near future.

Thanks for do this!!!

 

[bandit2013]

To do this justice and make it more apparent, the Vertical 212 or the Horizontal 212 is more forgiving than the OS Recto 412. I was also running the amp below its awesome point where the differences are definitive. In order to accomplish this I would have to use the attenuator in order to record using mics. That in itself does roll off the top end to some extent. Best advice is to just get a 12AT7 Jan type and hear for yourself. Also an SPAX7 in V1 helps too and aids in some of the harshness you may get running Crunch with the gain maxed out which was my way of getting similar tone to the Mark IV mode without getting that thin sound that CH3 seems to create. Also the brittleness of the Tweed setting on CH1 is reduced a tad. Only other solution is a Mullard 12AX7 long plate in V1 but that will also alter tone. Have not tried it in the amp since the V4 swap. Wonder what that will sound like.

 

[Giz-Tone]

Forgive my lack of knowledge on this topic; but wouldn't using a different pre amp tube than a 12AX7 in the Mark V damage the amp?